1. Field of the Invention
The present invention relates to computer graphics. More specifically, the present invention relates to displaying images on a display or viewfinder, and determining the distance to a viewer of the display in order to correctly render the perspective of an image on a projection plane.
2. Background Information
Viewing images in three dimensions typically requires that a "view volume" be specified in order to determine the appropriate rendering of images on a display screen. Much literature has been devoted towards the rendering of three-dimensional imagery, and especially with regards to the various perspectives and projections of images on a projection plane (see Foley, J., Van Dam, A., Feiner, S. K., and Hughes, John F., Computer Graphics, Principles and Practice (Second Edition, 1990) hereinafter "Foley and Van Dam," at pages 229-283). In order to accomplish projections from an image in three-dimensional space onto the projection plane, typically, using a perspective projection, the distance or hypothetical distance between the projection plane and the center of projection should be specified. This provides for a realistic representation of the perspective of the image on the projection plane or display as if the viewer was observing the real object which has been rendered. Typically, for applications wherein a user is seated at a workstation or similar environment, the distance from the projection plane to the center of projection is user definable for various effects. Distortion in perspective or scale with reference to the background is not a concern. In addition, this image need not be precisely correct, because the rendering of the image of this display may be viewed at various sizes and angles.
In at least one application, the variation of the distance between the center of projection for a 3-D image, and the projection plane may be important. For instance, in architecture, a 3-D perspective image of a building to be constructed may be rendered. In some instances, the architect may use three-dimensional models of the building to perform an evaluation of whether the building design must be modified in some manner prior to construction. This may include, among other things, a topographic construction of the environment (surrounding terrain and buildings) into which the new building is to be constructed. Again, this will provide an effective means for evaluating whether the building's design, or the surrounding landscaping must be modified in some manner prior to construction. Unfortunately, such models are typically expensive to create and are not cost effective for standard single-family homes.
Another way in which to evaluate the possible design of a building is to do a three-dimensional rendering of the image with its surrounding terrain and/or buildings. Again, as with the example of constructing models or other three-dimensional topographic views of the area, such computer-generated imagery may not be cost effective for a standard single-family construction. In addition, the rendering of the image may not be an accurate representation of the building to be constructed, and the environment into which it is to be built. This may be due to the fact that the screen is not of sufficient size to accurately render the image to cover the viewer's field of view, and the distance from the view projection plane to the center of the projection for the building may not be accurately known.